Grating coupling elements may be created in optical fiber claddings. In this field, the optical cladding of a fiber traditionally surrounds the fiber core and has a refractive index lower than that of the core to allow the propagation of a light wave in the core. Conjointly, the optical cladding permits the mechanical support of the core. The fiber core may not exist without the cladding.
Furthermore, the grating created in the fiber permits one or more guided modes to be coupled in the core of a fiber to one or more fiber cladding modes or vice versa.
C. Y. Lin and L. A. Wang, “Loss-tunable long period fibre grating made from etched corrugation structure,” Electron. Lett., 35 (21), (1999), pp. 1872–1873, illustrates a grating coupling element obtained by etching the cladding. However, the manufacturing process of this type of grating may be complex. For example, it may require the cladding to be etched, which may render the fiber fragile.
FIG. 1 shows a perspective view of an example of a coupling element in an optical fiber. The fiber 1 comprises a core 3 (shown in dotted lines) and a cladding 5; the latter has been etched Λ to create a grating R having a period Λ. The mechanical rigidity of the fiber may be modified by the etching 7 created in the cladding 5.
Furthermore, as the core of a fibre may not exist without the optical cladding, this dependence may restrict the possibilities of modifying the parameters of the cladding, and the gratings, as well as solutions for the design, architecture and integration of the coupling elements in complex systems.